JP2008072398A - Original illuminator, image reader, color original reader and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce illuminance unevenness in an original illuminator having a linear area to be illuminated than before. <P>SOLUTION: Light emitted from a LED 1 being a light source in which illuminance distribution shows, for example, a Lambert distribution is caused to pass through a lens array 2 configured by providing lenses having convergence in a line and is emitted onto a contact glass 3 (replaced with drawing seen from the front in Fig. 2 for convenience sake) being a plane to be illuminated. Curvature of an incident face R1 and an outgoing face R2 of the lens array 2 and a positional relation among the LED 1, the lens array 2 and the contact glass 3 are set to proper values. The LED 1 preferably emits white light by a single color or color mixture. The LED 1 can emit white light by a combination of LEDs of a plurality of different colors. A desirable result is obtained when central width is 2 mm in a reading area. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a document illuminating device used for a digital copying machine or an image scanner, and more particularly to a document illuminating device using a light emitting diode as a light source. The present invention also relates to an image reading apparatus including the original illumination device and an image forming apparatus including the image reading apparatus.

In recent years, light emitting diodes (hereinafter referred to as LEDs) are being actively developed, and the brightness of LED elements is rapidly increasing. LEDs generally have advantages such as long life, high efficiency, high G resistance, and monochromatic light emission, and are expected to be applied in many lighting fields.
As one of the applications, LEDs are used in a document illumination device of an image reading device such as a digital copying machine or an image scanner.

FIG. 7 is a schematic diagram of an image forming apparatus having the image reading apparatus as described above.
In the figure, the image forming apparatus has an image forming unit 100 and an image reading unit 200.

  The image forming unit 100 includes a drum-shaped latent image carrier 111, and a charging roller 112 as a charging unit, a developing device 113, a transfer roller 114, and a cleaning device 115 are disposed around the image forming unit 100. A “corona charger” can also be used as the charging means. Further, an optical scanning device 117 that receives external document information and performs optical scanning with the laser beam LB, such as the image reading unit 200, is provided, and “exposure by optical writing” is performed between the charging roller 112 and the developing device 113. Is supposed to do.

  When forming an image, the image carrier 111, which is a photoconductive photosensitive member, is rotated at a constant speed in the clockwise direction, the surface thereof is uniformly charged by the charging roller 112, and the optical beam of the laser beam LB of the optical scanning device 117 is written. An electrostatic latent image is formed upon exposure to the image. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed. The cassette 118 storing the transfer paper P is detachable from the main body of the image forming apparatus 100. When the transfer paper P is mounted as shown in the drawing, the uppermost sheet of the stored transfer paper P is fed by the paper supply roller 120. The leading edge of the fed transfer paper P is caught by the registration roller pair 119. The registration roller pair 119 feeds the transfer paper P to the transfer unit at the timing when the toner image on the image carrier 111 moves to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 114. The transfer paper P to which the toner image is transferred is sent to the fixing device 116, where the toner image is fixed by the fixing device 116, passes through the conveyance path 121, and is discharged onto the tray 123 by the discharge roller pair 122. The surface of the image carrier 111 after the toner image has been transferred is cleaned by a cleaning device 115 to remove residual toner, paper dust, and the like. The latent image carrier 111 is a photoconductive photoconductor, and an electrostatic latent image is formed by uniform charging and optical scanning, and the formed electrostatic latent image is visualized as a toner image.

  In the image reading unit 200, the document 202 is placed on the contact glass 201, and the document 202 is illuminated by an illumination unit (not shown) mounted on the first traveling body 203 disposed below the contact glass 201. The reflected light from the document 202 is reflected by the first mirror 203 a of the first traveling body 203, and then reflected by the first mirror 204 a and the second mirror 204 b of the second traveling body 204 and guided to the reduction imaging lens 205. The image is formed on the line sensor 206.

  When reading the longitudinal direction of the document, the first traveling body 203 moves to the right in the figure at a speed of V, and at the same time, the second traveling body 204 moves to the right at a speed 1/2 V that is half that of the first traveling body 203. To scan the entire document.

Usually, as a method of using LEDs as a document illumination device used in an image reading apparatus, a large number of LED elements are arranged and used in an array.
However, although LEDs have excellent characteristics as described above, since the absolute brightness of each element is insufficient for use as an illumination device of an image reading device, a low-speed reading device, It is mainly used for devices that emphasize compactness, and cold cathode fluorescent lamps are mainly used for high-speed reading devices and large devices.

  In order to compensate for this problem, it is common to increase the amount of light in the LED array by using a large number of LED elements constituting the LED array. However, since the light diffuses widely, it is not very efficient. It goes against power saving. In addition, when a bullet-like LED with less diffusion is used, the efficiency is increased, but the directivity is high and unevenness occurs in the main scanning direction.

  For the purpose of improving the light utilization efficiency, there is a proposal of a document illumination device combining an LED array and a long lens (see, for example, Patent Document 1 and Patent Document 2). Usually, the efficiency of the LED light has been increased by converging it on the sub-scan section of each LED. However, when such a method is used, there is a problem that the central portion of the convergent light is bright as shown in the drawing of Patent Document 1, and light is diffused and rapidly darkened at a position off the center. Since most of the emitted light from the LEDs has an angle in the sub-scanning cross section and is wasted, illuminance unevenness occurs in the main scanning direction unless a large number of LEDs are arranged.

  There is an invention of the present applicant that eliminates illuminance unevenness in the main scanning direction (see Patent Document 3). However, Patent Document 3 does not mention a condensing method in the sub-scanning direction. In addition, the present applicant has previously proposed a configuration in which an optical element has a light guide having an incident surface in the vicinity of a light beam exit surface of a point light source and an output surface facing the reading region (Patent Document 4). reference). According to this configuration, the target illuminance distribution can be obtained satisfactorily. However, since the reflector is used in addition to the light guide, the configuration is somewhat complicated, and the cost tends to increase accordingly.

Therefore, for the purpose of solving these problems, the present applicant appropriately arranges a plateau unit in which a plurality of rows of LEDs having a predetermined light distribution is installed, and a long lens that does not converge in the sub-scanning cross-sectional direction. A long lens that does not converge the emitted light on the sub-scanning section of each LED is appropriately disposed, and the emitted light of each LED is not mainly positioned on the document on the sub-scanning section of each LED but on the sub-scanning section. By converging to the document surface position having an angle in the scanning direction, the light convergence is high in the sub-scanning direction and the NA can be brightened. In the main scanning direction, the loss due to light diffusion is small and relatively small. A document illuminating device (see Patent Document 5) with little illuminance unevenness even with the number of LEDs has been proposed.
JP-A-11-232912 JP-A-8-111545 Japanese Patent Laid-Open No. 10-322521 JP 2004-361425 A JP-A-2005-278132

  However, although this invention (the invention disclosed in Patent Document 4) has the advantages as described above, it adopts a method of converging light sharply at the position of the original surface, which is caused by a deviation in the mounting angle of the long lens. There is a possibility that the amount of light reaching the line sensor light-receiving portion changes greatly due to the illumination position shift, and greatly affects the formed image. For this reason, in a digital copying machine or an image scanner, it is desirable to have a document illuminating device in which the illuminance distribution curve in the sub-scanning corresponding direction is somewhat wide, and the illuminance difference in the reading area does not occur even when the center position of the illumination is shifted from the reading unit. . For that purpose, in the vicinity of the maximum value of the illuminance distribution, a portion with a small illuminance unevenness that is a width (for example, 1 mm on one side) equal to or larger than a width necessary for reading plus a variation width due to a mechanical error, etc. There should be a part.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to reduce unevenness in illuminance in a document illumination device having a linear illuminated area, and to improve the quality of document and image reading.

  In order to achieve the above-mentioned object, the invention according to claim 1 is characterized in that an illuminated surface having a length and a width, the length direction as a main scanning direction, and the width direction as a sub-scanning direction. A light source unit in which a plurality of light emitting elements are arranged in a scanning direction; and a lens array that is disposed between the illuminated surface and the light source unit and includes a convergent lens, and the light flux from the light source unit Is irradiated onto the surface to be illuminated through the lens array.

  According to a second aspect of the present invention, in the document illuminating device according to the first aspect, one light emitting element is installed corresponding to each lens in the lens array, and the light emitting element is a white light emitting diode. To do.

  According to a third aspect of the present invention, in the original illuminating apparatus according to the first aspect, one light-emitting element is installed corresponding to each lens in the lens array, and the light-emitting elements emit two different colors. It is a white light emitting diode that emits white light by color mixture using the above chip.

  According to a fourth aspect of the present invention, in the document illuminating apparatus according to the first aspect, two or more light emitting elements are provided corresponding to each lens in the lens array, and the two or more light emitting elements are respectively It has the light emitting diode from which the color which light-emits differs, It is characterized by the above-mentioned.

  According to a fifth aspect of the present invention, in the original illuminating device according to the fourth aspect, one red light emitting diode, one green light emitting diode, and one blue light emitting diode are provided corresponding to each lens in the lens array. Features.

  According to a sixth aspect of the present invention, in the document illuminating device according to any one of the first to fifth aspects, each lens in the lens array is a lens having different curvatures in the main scanning section and the sub-scanning section. Features.

  According to a seventh aspect of the present invention, in the document illuminating device according to the sixth aspect, each lens in the lens array has at least one of the light incident surface and the light emitting surface of the main scanning section and the sub-scanning section having a non-cross section. It is a circle.

  According to an eighth aspect of the present invention, in the document illuminating device according to any one of the first to fifth aspects, at least one of the light incident surface and the light output surface of each lens in the lens array is a free-form surface. It is characterized by that.

  According to a ninth aspect of the present invention, in the document illuminating device according to any one of the first to eighth aspects, the material of the lens array is plastic.

  A tenth aspect of the present invention is an image reading apparatus using the original illumination device according to any one of the first to ninth aspects.

  According to an eleventh aspect of the present invention, there is provided a color original reading device using the original illumination device according to any one of the first to ninth aspects.

  A twelfth aspect of the invention is an image forming apparatus using the image reading device of the tenth aspect.

  A thirteenth aspect of the invention is an image forming apparatus using the color original reading device according to the eleventh aspect.

  According to the present invention, illuminance unevenness in a document illumination device having a linear illuminated area is further reduced as compared with the conventional art, and the quality of document and image reading can be improved.

Preferred embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
A first embodiment provided by the present invention includes a two-dimensional illuminated surface extending in the main scanning direction and the sub-scanning direction, a light source unit in which a plurality of light emitting elements are arranged in the main scanning direction, A document illuminating apparatus that includes a lens array that is disposed between an illumination surface and a light source unit thereof and includes a convergent lens, and that irradiates a surface to be illuminated with a light beam from the light source unit through the lens array.

  In the first embodiment, it is preferable that one light emitting element is installed corresponding to each lens in the lens array, and the light emitting element is a white light emitting diode. In this case, the light emitting diode may be of a type that emits white light by color mixing using two or more chips that emit different colors.

  In the first embodiment, instead of using a white light emitting diode as the light emitting element, it is also preferable to have a plurality of light emitting diodes (for example, red, green, and blue) that emit different colors.

  Regardless of the aspect of the first embodiment, each lens in the lens array is a lens having different curvatures in the main scanning section and the sub-scanning section. It is preferable that at least one of the emission surfaces has a non-circular cross section. Further, at least one of the light incident surface and the light emitting surface may be a free-form surface.

  Furthermore, regardless of the specific aspect of the first embodiment, the material of the lens array is preferably plastic.

  The first embodiment of the present invention described above will be described in more detail and specifically using Examples 1 and 2. Prior to the description of Examples 1 and 2, another preferred embodiment of the present invention will be described, and each element constituting Example 1 or 2 will be further described.

[Second Embodiment]
An image reading apparatus that is developed so as to incorporate the first embodiment is also one of the preferred embodiments provided by the present invention. In the present embodiment, it is preferable to be suitable for reading a color document. An example of the image reading apparatus according to the present embodiment is shown in the image reading unit 200 of FIG.

[Third Embodiment]
An image forming apparatus that is developed so as to incorporate the above-described second embodiment is also one of the preferred embodiments provided by the present invention. An example of the image forming apparatus according to the present embodiment is shown in FIG.

[Elements constituting the embodiment]
Hereinafter, in Example 1 or 2 for more specifically explaining the first embodiment, each element constituting each example will be described.
1 and 2 are views showing one lens in the lens array. In the following embodiments, one LED corresponds to each lens.

FIG. 1 is a diagram showing only a sub-scan section including a light source.
In FIG. 1, since the scanning optical system needs to optically read the surface to be illuminated, the scanning optical system is configured to illuminate obliquely and read from the front. In FIG. 1, light emitted from a light-emitting element 1 (preferably an LED) 1 is applied to the contact glass 3 through the lens 2.

FIG. 2 is a schematic view showing a cross section along the optical path including the principal ray.
In FIG. 2, only the contact glass 3 which is the surface to be illuminated is replaced with a view seen from the front. Such a diagram is hereinafter referred to as an irregular plan view for convenience. In FIG. 2, the light emitted from the light emitting element (preferably LED) 1 is irradiated to the contact glass 3 through the lens array 2.
1 and 2 also show the configuration of one lens in a lens array used in Example 1 described later.

  The contact glass 3 is formed of a glass plate having a width of 20 mm and a length of 50 mm, for example, and a central portion of about 2 mm in width is used as a reading area. The width in the sub-scanning direction of the CCD as the image reading means is approximately 1 mm in terms of the position of the illuminated area in the case of a three-color CCD. In consideration of component manufacturing errors, assembly errors, etc., the illumination width has a margin and the reading area is 2 mm. Therefore, if this area is set within an allowable range of uneven illuminance, a high-quality image can be obtained.

Illuminance unevenness uses the ratio of the difference between the maximum illuminance and the minimum illuminance to the maximum illuminance as a percentage, and the allowable value is preferably 12% or more when reading a color image. When reading monochrome images, up to about 30% is acceptable.
The chief ray is a ray passing through the optical axis of the lens, and usually the direction of emission of the maximum radiant energy of the light source is made to coincide with the optical axis of the lens.

FIG. 3 is a diagram illustrating an example in which the light distribution of the point light source is a Lambertian distribution.
In the same figure, the light emitted from the point light source 8 shows a Lambertian distribution like a light distribution 9.
The Lambert distribution is called when the intensity distribution of the light energy emitted from the point light source is spherical. The distribution in the figure shows a cross-sectional view (of a sphere). In the case of this distribution, the maximum energy is emitted in the direction normal to the surface of the light source. Assuming that the radiation direction of the maximum energy E is θ = 0 °, the optical energy of the luminous flux radiated in the angular direction decreases as θ increases, and becomes 1 / 2E (half value) of the maximum value at θh = 60 °. The solid angular energy emission is reduced by a factor of four.

Next, a light source that can be used in the present invention will be described.
In the present invention, the light source is most suitably a light emitting diode (LED). Among them, it is preferable to use a white LED in order to be able to handle reading of any document.

  There are several types of white LEDs. One of them is a one-chip type white LED using a phosphor. A light emitting unit called a chip is sealed in a transparent enclosing member mixed with a YAG phosphor. The chip emits blue light made of InGaN. Thereby, when the chip emits blue light, the phosphor is simultaneously excited to emit yellow fluorescence. Since blue and yellow are complementary to each other, when both go out together, they are recognized as white light.

As another type, there is a white light-emitting diode that does not use a phosphor and uses two or more chips that emit different colors and emits white light by color mixture. The plurality of chips are arranged on the same surface, and are combined to be recognized as white when all the emission colors are mixed.
For example, in the case of two chips, chips that emit blue and yellow light are used as described above. In the case of three chips, chips each emitting red, green and blue corresponding to so-called three primary colors are used.

  When using a white LED with a chip that emits white light, when using a white LED that emits white light with a mixture of multiple chips that emit different colors, when using a white LED with a different color, such as a combination of blue and yellow LEDs In the case of emitting white light with a color mixture of the above, any of the above configurations has the same effect that it can cope with reading of any document including a color document.

The specifications of this example are shown below.
<One lens in the lens array>
R1: Main scanning section is flat
Curvature radius of sub-scan section R = 10mm
R2: radius of curvature of main scanning section R = 5.925 mm cone multiplier K = −0.888
Curvature radius of sub-scan section R = 3.193 mm Conical multiplier K = −0.885
A ₄ = 0.00076
However, the R2 surface is both aspherical in the main scanning section and the sub-scanning section, and when the reciprocal of the recent radius of curvature (paraxial curvature) is C and the height from the optical axis is H, the following equation (several Defined in 1).

Center thickness: 7.73
Lens shape: The lens is a rectangular lens, and its size is 8 mm in the main scanning direction and 8 mm in the sub-scanning direction.
Material: nd = 1.491 vd = 57.2

<LED>
Light distribution: Lambert distribution Intensity distribution on the light emitting surface: Uniform Light emitting surface size: 0.3 (mm) x 0.3 (mm)
Quantity: 5 (pieces)
Efficiency: 1 (W) x 5
Emission wavelength: white consisting of the following three spectra, each weighting is as follows
450 nm: Weight 1
550 nm: weight 1
650 nm: weight 1
<Contact glass>
Center thickness: 3.2 (mm)
Material: nd = 1.517 vd = 64.2
<Position relationship>
From the R1 surface of the lens to the LED (on the optical axis of the lens): 1.81 mm
From the R2 surface of the lens to the contact glass (on the optical axis of the lens): 9.81 mm
Contact glass tilt with respect to the optical axis of the lens: 28.6 °
<Lighted surface (original surface)>
The contact glass surface is 20mm wide and 50mm long.

FIG. 4 is a diagram for explaining the illuminance distribution in the main scanning direction of the present embodiment.
In this figure, the light emitted from the light source in consideration of the light distribution is regarded as the illuminance of the area by the number of light incident on each area obtained by equally dividing the surface of the contact glass into a 1 mm square mesh. is there.

  Curves Gm1 and Gm2 represent the illuminance distribution in the main scanning direction by selecting the area having the highest illuminance on average in the main scanning direction at the approximate center of the illumination width and defining it as the central area of the illumination. Each curve represents a width of 1 mm in the sub-scanning direction. Therefore, the illuminance state with a reading area of 2 mm width can be seen from these two curves.

  The ratio of the minimum value of illuminance to the maximum value in the region of Gm1 to Gm2 was 95.7%. This is 4.3% in terms of illuminance unevenness, and the illuminance unevenness allowed when reading a color original is about 12%. In the present embodiment, a reading area having a width of 2 mm can be ensured.

FIG. 5 is a diagram for explaining the illuminance distribution in the sub-scanning direction of the present embodiment.
The figure shows the number of light rays emitted from the light source in consideration of the light distribution and entering each region obtained by equally dividing the surface of the contact glass into a mesh of 1 mm in the main scanning direction and 0.4 mm in the sub-scanning direction. Is regarded as the illuminance of the area.

  The illuminance distribution in the sub-scanning direction at the center position in the main scanning direction is a curve Gs1. The illuminance distribution at a position 3.6 mm away from the center position toward the end in the main scanning direction is the curve Gs2, and the illuminance distribution at a position further 3.6 mm (7.2 mm from the center) is the curve Gs3. Since the arrangement pitch of the lens and the LED is 14.5 mm, the illuminance distribution repeats substantially the same distribution at the same 14.5 mm. If the range of the main scanning direction region 0 to 7.2 mm is confirmed, almost the entire illuminance distribution can be estimated. However, it is a condition that the illuminance distribution in the main scanning direction is stable from end to end. The illuminance unevenness in the 7.2 mm width range is less than 3.8%. In this graph, it can be seen that a 50 mm × 2 mm area is a uniform illuminance area that can be used as a reading area.

The specifications of this example are shown below.
<One lens in the lens array>
Same as Example 1 <LED>
Light distribution: Lambert distribution Intensity distribution on the light emitting surface: Uniform Light emitting surface size: 0.3 (mm) x 0.3 (mm)
Quantity: 15 (pieces)
LED of emission wavelength 450nm x 5 (pieces)
5 x LEDs with emission wavelength of 550nm
5 x LEDs with emission wavelength of 650nm
Efficiency: 1 (W) x 15
<Contact glass>
Same as Example 1

FIG. 6 is an irregular plan view of the second embodiment.
In Example 2, the same lens array as in Example 1 was used, and an LED having an emission wavelength of 450 nm, an LED having an emission wavelength of 550 nm, and an LED having an emission wavelength of 650 nm were installed on each lens in the lens array at a pitch of 0.5 mm. Is.
With this configuration, it is possible to increase the illuminance on the document surface. Furthermore, since the light emission energy of each LED can be adjusted, it is possible to form an optimal light emission spectrum for a reading lens, a CCD, or an image processing device corresponding to the original illumination device.

It is a figure which shows only the sub-scan cross section containing the light source which is the principal part of the original illuminating device concerning one embodiment of this invention, and shows the structure of 1 lens in the lens array used for Example 1 of this invention. FIG. FIG. 1 is an irregular plan view schematically showing a cross section along an optical path including a principal ray, which is a main part of an original illumination device according to an embodiment of the present invention (a side view using a front view for convenience). FIG. 3 is a diagram showing a configuration of one lens in a lens array used in Example 1 of the present invention. It is a figure which shows the example whose light distribution of a point light source is a Lambert distribution of the original illuminating device which concerns on one embodiment of this invention. It is a figure for demonstrating the illuminance distribution of the main scanning direction of the original illuminating device which concerns on Example 1 of this invention. It is a figure for demonstrating the illumination intensity distribution of the subscanning direction of the original illuminating device which concerns on Example 1 of this invention. It is an irregular top view (side view which uses a front view for convenience for a part) of the original illuminating device concerning Example 2 of the present invention. 1 is a schematic diagram of an image forming apparatus that can suitably use an original illumination device according to an embodiment of the present invention.

Explanation of symbols

1 LED (or light emitting element)
2 Lens (or lens array)
DESCRIPTION OF SYMBOLS 3 Contact glass 8 Point light source 9 Light distribution 100 Image formation part 111 Latent image carrier 112 Charging roller 113 Developing device 114 Transfer roller 115 Cleaning device 117 Optical scanning device 118 Cassette 119 Registration roller pair 120 Paper feed roller 121 Conveyance path 122 Discharge Paper roller pair 123 Tray 200 Image reading unit 201 Contact glass 202 Document 203 First traveling body 203a First mirror 204 Second traveling body 204a First mirror 204b Second mirror 205 Reduction imaging lens 206 Line sensor

Claims (13)

An illuminated surface having a length and width;
A light source unit in which a plurality of light emitting elements are arranged in the main scanning direction when the length direction is a main scanning direction and the width direction is a sub-scanning direction;
A lens array that is arranged between the illuminated surface and the light source unit and is made of a convergent lens;
An original illuminating apparatus that irradiates the surface to be illuminated with a light beam from the light source unit through the lens array.   2. The document illuminating apparatus according to claim 1, wherein one light emitting element is installed corresponding to each lens in the lens array, and the light emitting element is a white light emitting diode.   One light emitting element is installed corresponding to each lens in the lens array, and the light emitting element is a white light emitting diode that emits white light by color mixture using two or more chips that emit different colors. The document illumination device according to claim 1, wherein:   The two or more light emitting elements are installed corresponding to each lens in the lens array, and each of the two or more light emitting elements has a light emitting diode having a different color. Document illumination device.   5. The document illuminating apparatus according to claim 4, wherein one red light emitting diode, one green light emitting diode, and one blue light emitting diode are provided for each lens in the lens array.   6. The document illuminating apparatus according to claim 1, wherein each lens in the lens array is a lens having different curvatures in a main scanning section and a sub-scanning section.   7. The document illumination device according to claim 6, wherein each lens in the lens array has a non-circular cross section at least one of the light incident surface and the light exit surface of the main scanning section and the sub-scanning section.   6. The document illumination device according to claim 1, wherein each lens in the lens array has at least one of a light incident surface and a light output surface being a free-form surface.   The document illumination device according to claim 1, wherein a material of the lens array is plastic.   An image reading apparatus using the document illumination device according to claim 1.   A color original reading apparatus using the original illumination device according to claim 1.   An image forming apparatus using the image reading apparatus according to claim 10.   An image forming apparatus using the color document reading device according to claim 11.

Images